<?php

if (! defined('BASEPATH'))
    exit('No direct script access allowed');

/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.1.6 or newer
 *
 * @package CodeIgniter
 * @author ExpressionEngine Dev Team
 * @copyright Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license http://codeigniter.com/user_guide/license.html
 * @link http://codeigniter.com
 * @since Version 1.0
 * @filesource
 *
 */
    
// ------------------------------------------------------------------------

/**
 * Security Class
 *
 * @package CodeIgniter
 * @subpackage Libraries
 * @category Security
 * @author ExpressionEngine Dev Team
 * @link http://codeigniter.com/user_guide/libraries/security.html
 */
class CI_Security
{

    /**
     * Random Hash for protecting URLs
     *
     * @var string
     * @access protected
     */
    protected $_xss_hash = '';

    /**
     * Random Hash for Cross Site Request Forgery Protection Cookie
     *
     * @var string
     * @access protected
     */
    protected $_csrf_hash = '';

    /**
     * Expiration time for Cross Site Request Forgery Protection Cookie
     * Defaults to two hours (in seconds)
     *
     * @var int
     * @access protected
     */
    protected $_csrf_expire = 7200;

    /**
     * Token name for Cross Site Request Forgery Protection Cookie
     *
     * @var string
     * @access protected
     */
    protected $_csrf_token_name = 'ci_csrf_token';

    /**
     * Cookie name for Cross Site Request Forgery Protection Cookie
     *
     * @var string
     * @access protected
     */
    protected $_csrf_cookie_name = 'ci_csrf_token';

    /**
     * List of never allowed strings
     *
     * @var array
     * @access protected
     */
    protected $_never_allowed_str = array(
            '[removed]',
            'document.write' => '[removed]',
            '.parentNode' => '[removed]',
            '.innerHTML' => '[removed]',
            'window.location' => '[removed]',
            '-moz-binding' => '[removed]',
            '<!--' => '&lt;!--',
            '-->' => '--&gt;',
            '<![CDATA[' => '&lt;![CDATA[',
            '<comment>' => '&lt;comment&gt;'
    );

    /* never allowed, regex replacement */
    /**
     * List of never allowed regex replacement
     *
     * @var array
     * @access protected
     */
    protected $_never_allowed_regex = array(
            'javascript\s*:',
            'expression\s*(\(|&\#40;)', // CSS and IE
            'vbscript\s*:', // IE, surprise!
            'Redirect\s+302',
            "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?"
    );

    /**
     * Constructor
     *
     * @return void
     */
    public function __construct ()
    {
        // Is CSRF protection enabled?
        if (config_item('csrf_protection') === TRUE) {
            // CSRF config
            foreach (array(
                    'csrf_expire',
                    'csrf_token_name',
                    'csrf_cookie_name'
            ) as $key) {
                if (FALSE !== ($val = config_item($key))) {
                    $this->{'_' . $key} = $val;
                }
            }
            
            // Append application specific cookie prefix
            if (config_item('cookie_prefix')) {
                $this->_csrf_cookie_name = config_item('cookie_prefix') .
                         $this->_csrf_cookie_name;
            }
            
            // Set the CSRF hash
            $this->_csrf_set_hash();
        }
        
        log_message('debug', "Security Class Initialized");
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Verify Cross Site Request Forgery Protection
     *
     * @return object
     */
    public function csrf_verify ()
    {
        // If it's not a POST request we will set the CSRF cookie
        if (strtoupper($_SERVER['REQUEST_METHOD']) !== 'POST') {
            return $this->csrf_set_cookie();
        }
        
        // Do the tokens exist in both the _POST and _COOKIE arrays?
        if (! isset($_POST[$this->_csrf_token_name], 
                $_COOKIE[$this->_csrf_cookie_name])) {
            $this->csrf_show_error();
        }
        
        // Do the tokens match?
        if ($_POST[$this->_csrf_token_name] != $_COOKIE[$this->_csrf_cookie_name]) {
            $this->csrf_show_error();
        }
        
        // We kill this since we're done and we don't want to
        // polute the _POST array
        unset($_POST[$this->_csrf_token_name]);
        
        // Nothing should last forever
        unset($_COOKIE[$this->_csrf_cookie_name]);
        $this->_csrf_set_hash();
        $this->csrf_set_cookie();
        
        log_message('debug', 'CSRF token verified');
        
        return $this;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Set Cross Site Request Forgery Protection Cookie
     *
     * @return object
     */
    public function csrf_set_cookie ()
    {
        $expire = time() + $this->_csrf_expire;
        $secure_cookie = (config_item('cookie_secure') === TRUE) ? 1 : 0;
        
        if ($secure_cookie &&
                 (empty($_SERVER['HTTPS']) or
                 strtolower($_SERVER['HTTPS']) === 'off')) {
            return FALSE;
        }
        
        setcookie($this->_csrf_cookie_name, $this->_csrf_hash, $expire, 
                config_item('cookie_path'), config_item('cookie_domain'), 
                $secure_cookie);
        
        log_message('debug', "CRSF cookie Set");
        
        return $this;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Show CSRF Error
     *
     * @return void
     */
    public function csrf_show_error ()
    {
        show_error('The action you have requested is not allowed.');
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Get CSRF Hash
     *
     * Getter Method
     *
     * @return string self::_csrf_hash
     */
    public function get_csrf_hash ()
    {
        return $this->_csrf_hash;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Get CSRF Token Name
     *
     * Getter Method
     *
     * @return string self::csrf_token_name
     */
    public function get_csrf_token_name ()
    {
        return $this->_csrf_token_name;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * XSS Clean
     *
     * Sanitizes data so that Cross Site Scripting Hacks can be
     * prevented. This function does a fair amount of work but
     * it is extremely thorough, designed to prevent even the
     * most obscure XSS attempts. Nothing is ever 100% foolproof,
     * of course, but I haven't been able to get anything passed
     * the filter.
     *
     * Note: This function should only be used to deal with data
     * upon submission. It's not something that should
     * be used for general runtime processing.
     *
     * This function was based in part on some code and ideas I
     * got from Bitflux: http://channel.bitflux.ch/wiki/XSS_Prevention
     *
     * To help develop this script I used this great list of
     * vulnerabilities along with a few other hacks I've
     * harvested from examining vulnerabilities in other programs:
     * http://ha.ckers.org/xss.html
     *
     * @param
     *            mixed string or array
     * @param
     *            bool
     * @return string
     */
    public function xss_clean ($str, $is_image = FALSE)
    {
        /*
         * Is the string an array?
         *
         */
        if (is_array($str)) {
            while (list ($key) = each($str)) {
                $str[$key] = $this->xss_clean($str[$key]);
            }
            
            return $str;
        }
        
        /*
         * Remove Invisible Characters
         */
        $str = remove_invisible_characters($str);
        
        // Validate Entities in URLs
        $str = $this->_validate_entities($str);
        
        /*
         * URL Decode
         *
         * Just in case stuff like this is submitted:
         *
         * <a
         * href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
         *
         * Note: Use rawurldecode() so it does not remove plus signs
         *
         */
        $str = rawurldecode($str);
        
        /*
         * Convert character entities to ASCII
         *
         * This permits our tests below to work reliably.
         * We only convert entities that are within tags since
         * these are the ones that will pose security problems.
         *
         */
        
        $str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", 
                array(
                        $this,
                        '_convert_attribute'
                ), $str);
        
        $str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", 
                array(
                        $this,
                        '_decode_entity'
                ), $str);
        
        /*
         * Remove Invisible Characters Again!
         */
        $str = remove_invisible_characters($str);
        
        /*
         * Convert all tabs to spaces
         *
         * This prevents strings like this: ja vascript
         * NOTE: we deal with spaces between characters later.
         * NOTE: preg_replace was found to be amazingly slow here on
         * large blocks of data, so we use str_replace.
         */
        
        if (strpos($str, "\t") !== FALSE) {
            $str = str_replace("\t", ' ', $str);
        }
        
        /*
         * Capture converted string for later comparison
         */
        $converted_string = $str;
        
        // Remove Strings that are never allowed
        $str = $this->_do_never_allowed($str);
        
        /*
         * Makes PHP tags safe
         *
         * Note: XML tags are inadvertently replaced too:
         *
         * <?xml
         *
         * But it doesn't seem to pose a problem.
         */
        if ($is_image === TRUE) {
            // Images have a tendency to have the PHP short opening and
            // closing tags every so often so we skip those and only
            // do the long opening tags.
            $str = preg_replace('/<\?(php)/i', "&lt;?\\1", $str);
        } else {
            $str = str_replace(array(
                    '<?',
                    '?' . '>'
            ), array(
                    '&lt;?',
                    '?&gt;'
            ), $str);
        }
        
        /*
         * Compact any exploded words
         *
         * This corrects words like: j a v a s c r i p t
         * These words are compacted back to their correct state.
         */
        $words = array(
                'javascript',
                'expression',
                'vbscript',
                'script',
                'base64',
                'applet',
                'alert',
                'document',
                'write',
                'cookie',
                'window'
        );
        
        foreach ($words as $word) {
            $temp = '';
            
            for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i ++) {
                $temp .= substr($word, $i, 1) . "\s*";
            }
            
            // We only want to do this when it is followed by a non-word
            // character
            // That way valid stuff like "dealer to" does not become "dealerto"
            $str = preg_replace_callback('#(' . substr($temp, 0, - 3) .
                     ')(\W)#is', array(
                            $this,
                            '_compact_exploded_words'
                    ), $str);
        }
        
        /*
         * Remove disallowed Javascript in links or img tags
         * We used to do some version comparisons and use of stripos for PHP5,
         * but it is dog slow compared to these simplified non-capturing
         * preg_match(), especially if the pattern exists in the string
         */
        do {
            $original = $str;
            
            if (preg_match("/<a/i", $str)) {
                $str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", 
                        array(
                                $this,
                                '_js_link_removal'
                        ), $str);
            }
            
            if (preg_match("/<img/i", $str)) {
                $str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", 
                        array(
                                $this,
                                '_js_img_removal'
                        ), $str);
            }
            
            if (preg_match("/script/i", $str) or preg_match("/xss/i", $str)) {
                $str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', 
                        $str);
            }
        } while ($original != $str);
        
        unset($original);
        
        // Remove evil attributes such as style, onclick and xmlns
        $str = $this->_remove_evil_attributes($str, $is_image);
        
        /*
         * Sanitize naughty HTML elements
         *
         * If a tag containing any of the words in the list
         * below is found, the tag gets converted to entities.
         *
         * So this: <blink>
         * Becomes: &lt;blink&gt;
         */
        $naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss';
        $str = preg_replace_callback(
                '#<(/*\s*)(' . $naughty . ')([^><]*)([><]*)#is', 
                array(
                        $this,
                        '_sanitize_naughty_html'
                ), $str);
        
        /*
         * Sanitize naughty scripting elements
         *
         * Similar to above, only instead of looking for
         * tags it looks for PHP and JavaScript commands
         * that are disallowed. Rather than removing the
         * code, it simply converts the parenthesis to entities
         * rendering the code un-executable.
         *
         * For example: eval('some code')
         * Becomes: eval&#40;'some code'&#41;
         */
        $str = preg_replace(
                '#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', 
                "\\1\\2&#40;\\3&#41;", $str);
        
        // Final clean up
        // This adds a bit of extra precaution in case
        // something got through the above filters
        $str = $this->_do_never_allowed($str);
        
        /*
         * Images are Handled in a Special Way
         * - Essentially, we want to know that after all of the character
         * conversion is done whether any unwanted, likely XSS, code was found.
         * If not, we return TRUE, as the image is clean.
         * However, if the string post-conversion does not matched the
         * string post-removal of XSS, then it fails, as there was unwanted XSS
         * code found and removed/changed during processing.
         */
        
        if ($is_image === TRUE) {
            return ($str == $converted_string) ? TRUE : FALSE;
        }
        
        log_message('debug', "XSS Filtering completed");
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Random Hash for protecting URLs
     *
     * @return string
     */
    public function xss_hash ()
    {
        if ($this->_xss_hash == '') {
            mt_srand();
            $this->_xss_hash = md5(time() + mt_rand(0, 1999999999));
        }
        
        return $this->_xss_hash;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * HTML Entities Decode
     *
     * This function is a replacement for html_entity_decode()
     *
     * The reason we are not using html_entity_decode() by itself is because
     * while it is not technically correct to leave out the semicolon
     * at the end of an entity most browsers will still interpret the entity
     * correctly. html_entity_decode() does not convert entities without
     * semicolons, so we are left with our own little solution here. Bummer.
     *
     * @param
     *            string
     * @param
     *            string
     * @return string
     */
    public function entity_decode ($str, $charset = 'UTF-8')
    {
        if (stristr($str, '&') === FALSE) {
            return $str;
        }
        
        $str = html_entity_decode($str, ENT_COMPAT, $charset);
        $str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', 
                $str);
        return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Filename Security
     *
     * @param
     *            string
     * @param
     *            bool
     * @return string
     */
    public function sanitize_filename ($str, $relative_path = FALSE)
    {
        $bad = array(
                "../",
                "<!--",
                "-->",
                "<",
                ">",
                "'",
                '"',
                '&',
                '$',
                '#',
                '{',
                '}',
                '[',
                ']',
                '=',
                ';',
                '?',
                "%20",
                "%22",
                "%3c", // <
                "%253c", // <
                "%3e", // >
                "%0e", // >
                "%28", // (
                "%29", // )
                "%2528", // (
                "%26", // &
                "%24", // $
                "%3f", // ?
                "%3b", // ;
                "%3d"
        ) // =
;
        
        if (! $relative_path) {
            $bad[] = './';
            $bad[] = '/';
        }
        
        $str = remove_invisible_characters($str, FALSE);
        return stripslashes(str_replace($bad, '', $str));
    }
    
    // ----------------------------------------------------------------
    
    /**
     * Compact Exploded Words
     *
     * Callback function for xss_clean() to remove whitespace from
     * things like j a v a s c r i p t
     *
     * @param
     *            type
     * @return type
     */
    protected function _compact_exploded_words ($matches)
    {
        return preg_replace('/\s+/s', '', $matches[1]) . $matches[2];
    }
    
    // --------------------------------------------------------------------
    
    /*
     * Remove Evil HTML Attributes (like evenhandlers and style)
     *
     * It removes the evil attribute and either:
     * - Everything up until a space
     * For example, everything between the pipes:
     * <a |style=document.write('hello');alert('world');| class=link>
     * - Everything inside the quotes
     * For example, everything between the pipes:
     * <a |style="document.write('hello'); alert('world');"| class="link">
     *
     * @param string $str The string to check
     * @param boolean $is_image TRUE if this is an image
     * @return string The string with the evil attributes removed
     */
    protected function _remove_evil_attributes ($str, $is_image)
    {
        // All javascript event handlers (e.g. onload, onclick, onmouseover),
        // style, and xmlns
        $evil_attributes = array(
                'on\w*',
                'style',
                'xmlns',
                'formaction'
        );
        
        if ($is_image === TRUE) {
            /*
             * Adobe Photoshop puts XML metadata into JFIF images,
             * including namespacing, so we have to allow this for images.
             */
            unset($evil_attributes[array_search('xmlns', $evil_attributes)]);
        }
        
        do {
            $count = 0;
            $attribs = array();
            
            // find occurrences of illegal attribute strings without quotes
            preg_match_all(
                    '/(' . implode('|', $evil_attributes) .
                             ')\s*=\s*([^\s>]*)/is', $str, $matches, 
                            PREG_SET_ORDER);
            
            foreach ($matches as $attr) {
                
                $attribs[] = preg_quote($attr[0], '/');
            }
            
            // find occurrences of illegal attribute strings with quotes (042
            // and 047 are octal quotes)
            preg_match_all(
                    "/(" . implode('|', $evil_attributes) .
                             ")\s*=\s*(\042|\047)([^\\2]*?)(\\2)/is", $str, 
                            $matches, PREG_SET_ORDER);
            
            foreach ($matches as $attr) {
                $attribs[] = preg_quote($attr[0], '/');
            }
            
            // replace illegal attribute strings that are inside an html tag
            if (count($attribs) > 0) {
                $str = preg_replace(
                        "/<(\/?[^><]+?)([^A-Za-z<>\-])(.*?)(" .
                                 implode('|', $attribs) .
                                 ")(.*?)([\s><])([><]*)/i", '<$1 $3$5$6$7', $str, 
                                - 1, $count);
            }
        } while ($count);
        
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Sanitize Naughty HTML
     *
     * Callback function for xss_clean() to remove naughty HTML elements
     *
     * @param
     *            array
     * @return string
     */
    protected function _sanitize_naughty_html ($matches)
    {
        // encode opening brace
        $str = '&lt;' . $matches[1] . $matches[2] . $matches[3];
        
        // encode captured opening or closing brace to prevent recursive vectors
        $str .= str_replace(array(
                '>',
                '<'
        ), array(
                '&gt;',
                '&lt;'
        ), $matches[4]);
        
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * JS Link Removal
     *
     * Callback function for xss_clean() to sanitize links
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on link-heavy strings
     *
     * @param
     *            array
     * @return string
     */
    protected function _js_link_removal ($match)
    {
        return str_replace($match[1], 
                preg_replace(
                        '#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si', 
                        '', 
                        $this->_filter_attributes(
                                str_replace(array(
                                        '<',
                                        '>'
                                ), '', $match[1]))), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * JS Image Removal
     *
     * Callback function for xss_clean() to sanitize image tags
     * This limits the PCRE backtracks, making it more performance friendly
     * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
     * PHP 5.2+ on image tag heavy strings
     *
     * @param
     *            array
     * @return string
     */
    protected function _js_img_removal ($match)
    {
        return str_replace($match[1], 
                preg_replace(
                        '#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si', 
                        '', 
                        $this->_filter_attributes(
                                str_replace(array(
                                        '<',
                                        '>'
                                ), '', $match[1]))), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Attribute Conversion
     *
     * Used as a callback for XSS Clean
     *
     * @param
     *            array
     * @return string
     */
    protected function _convert_attribute ($match)
    {
        return str_replace(array(
                '>',
                '<',
                '\\'
        ), array(
                '&gt;',
                '&lt;',
                '\\\\'
        ), $match[0]);
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Filter Attributes
     *
     * Filters tag attributes for consistency and safety
     *
     * @param
     *            string
     * @return string
     */
    protected function _filter_attributes ($str)
    {
        $out = '';
        
        if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', 
                $str, $matches)) {
            foreach ($matches[0] as $match) {
                $out .= preg_replace("#/\*.*?\*/#s", '', $match);
            }
        }
        
        return $out;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * HTML Entity Decode Callback
     *
     * Used as a callback for XSS Clean
     *
     * @param
     *            array
     * @return string
     */
    protected function _decode_entity ($match)
    {
        return $this->entity_decode($match[0], 
                strtoupper(config_item('charset')));
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Validate URL entities
     *
     * Called by xss_clean()
     *
     * @param
     *            string
     * @return string
     */
    protected function _validate_entities ($str)
    {
        /*
         * Protect GET variables in URLs
         */
        
        // 901119URL5918AMP18930PROTECT8198
        $str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', 
                $this->xss_hash() . "\\1=\\2", $str);
        
        /*
         * Validate standard character entities
         *
         * Add a semicolon if missing. We do this to enable
         * the conversion of entities to ASCII later.
         *
         */
        $str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", 
                $str);
        
        /*
         * Validate UTF16 two byte encoding (x00)
         *
         * Just as above, adds a semicolon if missing.
         *
         */
        $str = preg_replace('#(&\#x?)([0-9A-F]+);?#i', "\\1\\2;", $str);
        
        /*
         * Un-Protect GET variables in URLs
         */
        $str = str_replace($this->xss_hash(), '&', $str);
        
        return $str;
    }
    
    // ----------------------------------------------------------------------
    
    /**
     * Do Never Allowed
     *
     * A utility function for xss_clean()
     *
     * @param
     *            string
     * @return string
     */
    protected function _do_never_allowed ($str)
    {
        $str = str_replace(array_keys($this->_never_allowed_str), 
                $this->_never_allowed_str, $str);
        
        foreach ($this->_never_allowed_regex as $regex) {
            $str = preg_replace('#' . $regex . '#is', '[removed]', $str);
        }
        
        return $str;
    }
    
    // --------------------------------------------------------------------
    
    /**
     * Set Cross Site Request Forgery Protection Cookie
     *
     * @return string
     */
    protected function _csrf_set_hash ()
    {
        if ($this->_csrf_hash == '') {
            // If the cookie exists we will use it's value.
            // We don't necessarily want to regenerate it with
            // each page load since a page could contain embedded
            // sub-pages causing this feature to fail
            if (isset($_COOKIE[$this->_csrf_cookie_name]) &&
                     preg_match('#^[0-9a-f]{32}$#iS', 
                            $_COOKIE[$this->_csrf_cookie_name]) === 1) {
                return $this->_csrf_hash = $_COOKIE[$this->_csrf_cookie_name];
            }
            
            return $this->_csrf_hash = md5(uniqid(rand(), TRUE));
        }
        
        return $this->_csrf_hash;
    }
}

/* End of file Security.php */
/* Location: ./system/libraries/Security.php */